Natural products are the ideal small molecules to moderate biological processes, but some of their traditional liabilities could prevent their broad adoption in modem screening programs. This proposal deals with various ways of finding and exploring natural products with two overall goals: finding new biologically active natural products and developing natural product libraries. Specific aims are: 1. Characterize biologically active natural products and their targets. This specific aim covers a fairly traditional approach to natural products emphasizing unusual organisms. Organismal sources include endophytic fungi, insects, and root exudates of higher plants. Structure determinations of small molecules both alone and bound to their protein targets will be done with X-ray crystallography. 2. Determine the biosynthetic pathways for arrays of structurally diverse natural products. Some organisms produce families of structurally diverse natural products. This proposal will focus on two extraordinary cases: a) the pantocin family of antibiotics produced by Erwinia herbicola (Pantoea agglomerans) and b) the guanacastepene family of diterpenes elaborated by an endophytic fungus from Costa Rica. Understanding the structure of the biosynthetic pathway(s) leading to a natural product library will lead to a deeper appreciation of how biosynthetic complexity and regulation are genetically encoded. 3. Produce novel natural products by screening heterologously expressed environmental DNA (eDNA). Soil microbes, especially members of the actinomycete family; grown in laboratory culture have been a mainstay of natural products chemistry and the pharmaceutical industry. Recent work has shown that only a tiny (0 1 percent) and statistically biased fraction of soil microbes can be grown in laboratory culture. The uncultured majority of soil microbes, which should also produce natural products, are the largest source of untapped genetic diversity on the planet. Approaches to accessing and screening these natural products by heterologously expressing DNA obtained directly from the environment, eDNA, will be developed.